1. Field of the Invention
The present invention relates to a projection apparatus.
2. Description of the Related Art
Conventionally, as a projection apparatus, there has been known an apparatus that projects, onto a screen, an image generated by a liquid crystal display element. This type of projection apparatus generally has a light source and a liquid crystal display element, and flicker occurs in each of them.
For example, the light source causes continuous flicker in a projection image due to temperature change, electrode form change, or fluctuation in voltage applied to the light source. To cope with this, Japanese Laid-Open Patent Publication (Kokai) No. 2005-037455 presents the technique that when a fluctuation in the light quantity of the light source is detected, electrical power of the light source is increased step by step, and after a fluctuation in the light quantity of the light source becomes undetected, electrical power of the light source is decreased step by step toward an initial value of light source electrical power. There has been known another method which adjusts an aperture of the light source.
As a means to reduce flicker caused by the liquid crystal display element, there has been known a method that an opposing electrode voltage Vcom applied to a common electrode opposed to pixel electrodes is adjusted in a final stage or the like of a manufacturing process. However, during actual operations, flicker occurs due to instability of the opposing electrode voltage Vcom in an early stage of the activation of the liquid crystal display element, deviation of the central pixel potential caused by signal waveform distortion in the liquid crystal display element, or the like (for example, Japanese Laid-Open Patent Publication (Kokai) No. 2002-091391).
There has been another method which reduces flicker by controlling the quantity of light in a luminance modulation liquid crystal display element.
In the conventional methods, flicker caused by the light source is reduced using a flicker reduction means of the liquid crystal display element, or flicker caused by the liquid crystal display element is reduced using a flicker reduction means of a light source drive unit.
However, because the luminance modulation liquid crystal display element reduces flicker by reducing contrast, it produces no effect of reducing flicker caused by the light source. Also, flicker control through adjustment of the liquid-crystal opposing electrode voltage Vcom produces no effect of reducing flicker caused by the light source.
The method that reduces flicker caused by the light source by adjusting light beams output from the light source using an aperture or by adjusting light source drive electrical power cannot cope with flicker occurring asynchronously in a plurality of liquid crystal display elements. This method also has the disadvantage that adjustments are made by lowering luminance although the problem does not lie in the light source.